Drive shaft, in particular radial shaft for a gas-turbine engine

ABSTRACT

A drive shaft, in particular a radial shaft for a gas-turbine engine, includes a metallic and hollow shaft shank  1  with load transfer elements  2, 10, 11  integrally formed onto its ends. The shaft shank  1  includes a metal tube  3, 9  prefabricated as a semi-finished part, designed only for transmission of torsional loads and having a constant wall thickness. An outer or inner reinforcement  5, 8  intended only for ensuring the necessary bending stiffness is provided on the outer and/or inner circumferential surface of the metal tube  3, 9  and made from a fiber-composite layer  13, 13 ′ with fibers oriented in the longitudinal direction of the drive shaft. The inner fiber-composite layer  13  acting as outer reinforcement  5  is sheathed with an outer fiber-composite layer  14  made from fibers oriented at an angle of 60° to 90° relative to the longitudinal direction.

This application claims priority to German Patent ApplicationDE102010048926.3 filed Oct. 19, 2010, the entirety of which isincorporated by reference herein.

This invention relates to a high-speed drive shaft, in particular to aradial shaft for a gas-turbine engine, including a metallic and hollowshaft shank with load transfer elements integrally formed onto its ends.

The radial shaft of a gas-turbine engine provided for driving agenerator is usually designed as hollow-bored and honed metalliccomponent with load transfer elements integrally formed onto its twoends. The connection to the engine or the generator, respectively, ismade via the load transfer elements, for example provided with toothing,with the interconnection of a transmission. The manufacture of the knownmetallic radial shafts for gas-turbine engines involves heavy cost,since their tube cross-section varies to achieve a high bendingstiffness and a correspondingly high critical bending speed, requiringexpensive boring and honing processes. To minimize production-relatedimbalances and the bending stresses involved, high-precision and henceexpensive balancing is also necessary. In addition, the high costs setlimits on the frequently desired use of radial shafts at higheroperating speed and/or with greater length and also with correspondinglyhigher bending stiffness and critical bending speed.

The suggestion has already been made to produce the radial shaft ofgas-turbine engines completely from fiber-composite material or in ahybrid design using a tube made of fiber-composite material withmetallic load transfer elements attached to its ends. However, aneffective increase of the critical bending speed is not assured due tothe reduced bending stiffness compared with a radial shaft made ofmetal. In addition, the torsional loads that are effective particularlyin the area of the load transfer lead to critical stress conditions inthe fiber-composite material.

The present invention, in a broad aspect, provides a radial shaft withhigh bending stiffness and high critical bending speed which can beproduced inexpensively and operated in an increased speed range evenwith greater length.

The underlying idea of the invention is to provide for decoupling of thetorsional load transmission and flexural stiffening of the drive shaftin that the shaft shank provided at the ends with load transfer elementsincludes a metal tube prefabricated as a semi-finished part, designedonly for transmission of torsional loads and having a constant wallthickness, and an outer or inner reinforcement intended only forensuring the necessary bending stiffness on the outer or innercircumferential surface of the metal tube and made from afiber-composite layer with fibers oriented in the longitudinal directionof the drive shaft, where the fiber-composite layer acting as the outerreinforcement is sheathed with an outer fiber-composite layer made fromfibers oriented at an angle of 60° to 90° relative to the longitudinaldirection.

The high-speed drive shaft thus formed and intended in particular as aradial shaft for a gas-turbine engine can be manufactured at low cost.The outer or inner reinforcement made of fiber-composite material forthe metal tube designed only for torque transmission and hence slenderensures such a high flexural stiffening that longer drive shafts withhigher operating speed can be used thanks to a resultant significantincrease in the critical bending speed at the same torque. Its use as aradial shaft thus results in new possibilities for engine design.

In a further embodiment of the present invention, the fiber-compositelayer formed out of axially oriented fibers is made of fiber-compositematerial compressed into half-shells, so that a high fiber density andhence an even higher bending stiffness can be achieved.

An intermediate layer designed as a sliding layer to compensate forheat-related longitudinal expansions is provided between the metal tubeand the fiber-composite layer contacting the metal tube. Theintermediate layer can also be designed as an adhesive layer, as anelastic layer and/or as a corrosion-preventing layer.

In accordance with yet another feature of the invention, the innerfiber-composite layer of the outer reinforcement is fixed in thelongitudinal direction by a positioning ring provided centrally on theouter circumference of the metal tube.

In a further embodiment of the invention, the fiber-composite layeracting as inner reinforcement is fixed by covers fitted on both sidesinside the metal tube which at the same time prevent any passage ofliquid through the metal tube and protect the fiber-composite layer fromexternal effects.

The fiber-composite layers are made of, in an advantageous embodiment ofthe invention, glass, carbon and/or aramide fibers embedded into apolymer matrix.

In a further embodiment, the metal tube is designed as a straight orconically tapering tube of circular cross-section.

The load transfer elements, for example provided with outer toothing,are preferably produced separately and connected to the ends of themetal tube by welding, in particular friction welding.

The present invention is more fully described in light of theaccompanying drawings showing preferred embodiments. In the drawings,

FIG. 1 shows a longitudinal section of a radial shaft of themetal/fiber-composite/hybrid design with an outer fiber-compositereinforcement for a gas-turbine engine,

FIG. 2 shows an enlarged sectional view of a wall section of the radialshaft as per FIG. 1,

FIG. 2A shows a partial cut-away view of the radial shaft per FIG. 1,

FIG. 3 shows a longitudinal section of a radial shaft of the hybriddesign with an inner fiber-composite reinforcement in a conicallydesigned metal tube,

FIG. 4 shows an enlarged view of the positioning ring of the radialshaft of FIG. 1,

FIG. 5 shows a sectional view of the radial shaft of FIG. 3 taken alongsection line 5-5, and

FIG. 6 shows a further embodiment of the radial shaft of FIG. 1.

The radial shaft shown in FIG. 1 includes a shaft shank 1 with loadtransfer elements 2 provided at its ends. The shaft shank 1 includes ametal tube 3 configured as a prefabricated semi-finished part and havingcircular cross-section, constant wall thickness and constant diameter,onto the ends of which shank the load transfer elements 2, in this casehaving an outer toothing 4, are integrally formed or attached. Theseparately produced load transfer elements 2 are connected to the metaltube 3, which is intended only for transmitting torsional loads and hascorrespondingly slender dimensions, for example by friction welding. Itis however also conceivable that the load transfer elements 2 are anintegral part of the metal tube. The required bending stiffness of theshaft shank 1 is obtained by an outer reinforcement 5 fitted to theouter circumference of the metal tube 3 and made from an (inner)fiber-composite layer 13 with fibers oriented predominantly in thelongitudinal direction of the shaft shank 1. The inner fiber-compositelayer 13 of axially oriented fibers is sheathed with an outerfiber-composite layer 14 made of fibers oriented at an angle of 60° tonearly 90°, in order to prevent thereby any radial widening of the outerreinforcement 5, i.e. the inner fiber-composite layer 13, caused bybending. See FIG. 2A.

The inner fiber-composite layer 13 includes, in accordance with thepresent embodiment, two prefabricated half-shells (see, for example,FIG. 5) of fiber-composite material placed around the metal tube 3. Thehalf-shells of fiber-composite material are manufactured in acompression process in a mould such that a high fiber content and hencea high stiffness can be achieved. Then the outer fiber-composite layer14 is applied. The fiber-composite material is made of glass, carbon oraramide fibers embedded into a polymer matrix, including for example athermoplastic or thermosetting plastic. Between the outer reinforcement5 and the metal tube 3 is an intermediate layer 6—of PTFE paint in thepresent exemplary embodiment—provided on the outer surface of the metaltube 3 in order to compensate for any thermally related longitudinalexpansion of the metal tube 3. An intermediate layer 6 made of a polymeror elastomer can furthermore also have an adhesive orcorrosion-preventing or elastic effect. See FIG. 6 showing such anintermediate layer 6. For fixing the outer reinforcement 5 made offiber-composite material, the middle of the metal tube 3 is providedwith a positioning ring 7 extending in its circumferential direction.See the enlarged view of the positioning ring 7 shown in FIG. 4. Thepreviously described wall structure of a metal tube 3 forming the shaftshank 1 with outer reinforcement 5 is shown in enlarged representationin FIG. 2.

Instead of the outer reinforcement 5, an inner reinforcement 8 can alsobe applied to the inner circumferential surface of the metal tube 3which is like the outer reinforcement 5—however without fiber-compositelayer 14—and therefore, has a fiber-composite layer 13 with axiallyoriented fibres.

FIG. 3 shows a shaft shank 1 with an inner reinforcement 8 applied tothe inner circumferential surface of a conically tapering metal tube 9prefabricated as a semi-finished part. The separately produced loadtransfer elements 10, 11 welded to the tube ends are of differing sizedue to the conical design of the metal tube 9. A cover 12 held at eachend of the inner reinforcement 8 inside the shaft shank 1 fixes thefiber-composite material of the inner reinforcement 8 inside the conicalmetal tube 9 and furthermore prevents any passage of liquid through theradial shaft and any damage that this might entail to the innerreinforcement 8 made of the fiber-composite layer 13′. The innerreinforcement 8 with fiber composite layer 13 can be provided as twoprefabricated half-shells as shown in FIG. 5.

Thanks to the formation of the previously described radial shaft from aprefabricated simple metal tube as a semi-finished part and from anouter or inner reinforcement, respectively, of fiber-composite material,and also thanks to the expensive balancing measures required forconventional radial shafts no longer being needed, the costs ofmanufacture are low. The metal tube is designed only for thetransmission of torsional loads and has a correspondingly low mass andcomparatively low diameter, whereas the bending stiffness required for ahigh speed is assured by the inner or outer reinforcement consisting oflightweight fiber-composite material. Thanks to the resultantsignificant increase in the critical bending speed, it is possible tomanufacture also longer radial shafts inexpensively and in addition tooperate them at higher speeds. For example, a radial shaft of 0.5 mlength previously operated with 15,000 to 25,000 revolutions per secondcan in the embodiment described above be designed twice as long andoperated at a speed of up to 45,000 revolutions per second.

LIST OF REFERENCE NUMERALS

-   1 Shaft shank-   2 Load transfer elements of 3-   3 Metal tube of 1-   4 Outer toothing of 2, 10, 11-   5 Outer reinforcement of 3-   6 Intermediate layer-   7 Positioning ring-   8 Inner reinforcement of 9-   9 Conically tapering metal tube-   10 Load transfer element of 9-   11 Load transfer element of 9-   12 Cover of 9-   13, 13′ inner fiber-composite layer of 5 or 8, respectively-   14 Outer fiber-composite layer

What is claimed is:
 1. A drive shaft, comprising: a metallic and hollowshaft shank having load transfer elements integrally formed onto itsends, the shaft shank including: a metal tube prefabricated as asemi-finished part, configured for transmission of torsional loads andhaving a constant wall thickness, and a reinforcement layer positionedon an exterior of the metal tube configured for ensuring a bendingstiffness on the surface of the metal tube, the reinforcement layerhaving an inner fiber-composite layer with fibers oriented in alongitudinal direction of the drive shaft, wherein, the reinforcementlayer includes an outer fiber-composite layer having fibers oriented atan angle of 60° to 90° relative to the longitudinal direction; anintermediate layer provided between the metal tube and the innerfiber-composite layer; wherein the intermediate layer is configured as asliding layer to compensate for heat-related longitudinal expansions. 2.The drive shaft of claim 1, wherein the intermediate layer is configuredas at least one chosen from an elastic layer and a corrosion-preventinglayer.
 3. The drive shaft of claim 1, and further comprising a radiallyprojecting positioning ring provided centrally on the outercircumference of the metal tube for fixing the inner fiber-compositelayer in a longitudinal direction on the exterior of the metal tube. 4.The drive shaft of claim 1, and further comprising covers fitted on bothsides inside the metal tube for fixing the inner fiber-composite layerin a longitudinal direction on the interior of the metal tube while alsosealing the metal tube to prevent passage of liquid through the metaltube and protect the inner fiber-composite layer from external effects.5. The drive shaft of claim 1, wherein the metal tube is configured asone chosen from a straight and a conically tapering tube of circularcross-section.
 6. The drive shaft of claim 1, and further comprisingseparately produced load transfer elements connected to ends of themetal tube by welding.
 7. The drive shaft of claim 1, wherein the driveshaft is a radial shaft for a gas-turbine engine.
 8. A drive shaft,comprising: a metallic and hollow shaft shank having load transferelements integrally formed onto its ends, the shaft shank including: ametal tube prefabricated as a semi-finished part, configured fortransmission of torsional loads and having a constant wall thickness,and a reinforcement layer positioned on an interior of the metal tubeconfigured for ensuring a bending stiffness on the surface of the metaltube, the reinforcement layer having an inner fiber-composite layer withfibers oriented in a longitudinal direction of the drive shaft; anintermediate layer provided between the metal tube and the innerfiber-composite layer; wherein the intermediate layer is configured as asliding layer to compensate for heat-related longitudinal expansions. 9.The drive shaft of claim 8, wherein the inner fiber-composite layer ismade of fiber-composite material compressed into half-shells.
 10. Thedrive shaft of claim 8, wherein the intermediate layer is configured asat least one chosen from an elastic layer and a corrosion-preventinglayer.
 11. The drive shaft of claim 8, and further comprising coversfitted on both sides inside the metal tube for fixing the innerfiber-composite layer in a longitudinal direction on the interior of themetal tube while also sealing the metal tube to prevent passage ofliquid through the metal tube and protect the inner fiber-compositelayer from external effects.
 12. The drive shaft of claim 8, wherein themetal tube is configured as one chosen from a straight and a conicallytapering tube of circular cross-section.
 13. The drive shaft of claim 8,and further comprising separately produced load transfer elementsconnected to ends of the metal tube by welding.
 14. The drive shaft ofclaim 8, wherein the drive shaft is a radial shaft for a gas-turbineengine.
 15. A drive shaft, comprising: a metallic and hollow shaft shankhaving load transfer elements integrally formed onto its ends, the shaftshank including: a metal tube prefabricated as a semi-finished part,configured for transmission of torsional loads and having a constantwall thickness, and a reinforcement layer positioned on an exterior ofthe metal tube configured for ensuring a bending stiffness on thesurface of the metal tube, the reinforcement layer having an innerfiber-composite layer with fibers oriented in a longitudinal directionof the drive shaft, wherein the reinforcement layer includes an outerfiber-composite layer having fibers oriented at an angle of 60° to 90°relative to the longitudinal direction; a radially projectingpositioning ring provided centrally on the outer circumference of themetal tube for fixing the inner fiber-composite layer in a longitudinaldirection on the exterior of the metal tube.
 16. The drive shaft ofclaim 15, and further comprising an intermediate layer provided betweenthe metal tube and the inner fiber-composite layer; wherein theintermediate layer is configured as at least one chosen from an adhesivelayer, an elastic layer and a corrosion-preventing layer.
 17. The driveshaft of claim 15, and further comprising covers fitted on both sidesinside the metal tube for fixing the inner fiber-composite layer in alongitudinal direction on the interior of the metal tube while alsosealing the metal tube to prevent passage of liquid through the metaltube and protect the inner fiber-composite layer from external effects.18. The drive shaft of claim 15, wherein the metal tube is configured asone chosen from a straight and a conically tapering tube of circularcross-section.